COMPARISON OF TRANSMISSION THROUGH OLIGOSYNAPTIC CUTANEOUS AND MUSCLE AFFERENT REFLEX PATHWAYS DURING FICTIVE LOCOMOTION AND SCRATCHING IN THE DECEREBRATE CAT. A. M. Degtyarenko, E. S. Simon, T. Norden-Krichmar, and R. E. Burke. Laboratory of Neural Control, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892.
APStracts 4:238N, 1997.
ABSTRACT
We have compared state-dependent transmission through oligosynaptic (minimally disynaptic) reflex pathways from low-threshold cutaneous and muscle afferents to some flexor and extensor lumbosacral motoneurons during fictive locomotion and scratching in decerebrate unanesthetized cats. As reported in earlier work, oligosynaptic cutaneous excitatory postsynaptic potentials (EPSPs) in flexor digitorum longus (FDL) and inhibitory postsynaptic potentials (IPSPs) in extensor digitorum (EDL) longus motoneurons were markedly enhanced during the early flexion phase of fictive locomotion. We show in this paper that, in contrast, these cutaneous reflex pathways were markedly depressed during all phases of fictive scratching. On the other hand, disynaptic EPSPs produced by homonymous and synergist group I muscle afferents in flexor (TA and EDL) motoneurons were present and strongly modulated during both fictive locomotion and scratching. During both actions, these disynaptic group I EPSPs appeared or exhibited the largest amplitude when the motoneuron membrane potential was most depolarized and the parent motor pool was active. 4. There was an INTERESTING exception to the simple pattern of coincident group I EPSP enhancement and motoneuron depolarization. During locomotion, disynaptic group I EPSPs in both FDL and flexor hallucis longus (FHL) motoneurons cells were facilitated during the extension phase, although FDL motoneurons were relatively hyperpolarized while FHL cells were depolarized. The reverse situation was found during fictive scratching; group I EPSPs were facilitated in both FDL and FHL cells during the flexion phase, when FDL motoneurons were depolarized and FHL cells were relatively hyperpolarized. These observations suggest that the disynaptic EPSPs in these two motor nuclei are produced by common interneurons. 5. Reciprocal disynaptic inhibitory pathways from group Ia muscle afferents to antagonist motoneurons were also active and subject to phase-dependent modulation during both fictive locomotion and scratching. In all but one cell tested, reciprocal disynaptic group Ia IPSPs were largest during those phases in which the motoneuron membrane potential was relatively hyperpolarized and the parent motor pool was inactive. 6. Oligosynaptic PSPs in motoneurons produced by stimulation of the mesencephalic locomotor region (MLR) were strongly modulated during fictive locomotion but were powerfully suppressed throughout fictive scratching. Large cord dorsum potentials generated by MLR stimuli were also markedly suppressed during fictive scratching. These results allow certain inferences about the organization of interneurons in the pathways examined. They also suggest that the CPGs that produce fictive locomotion and scratching are organized differently. 

Received 10 June 1997; accepted in final form 8 September 1997.
APS Manuscript Number J472-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 7 October 1997